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Old 12-30-2012, 07:58 PM   #1 (permalink)
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Clogged carb or low idle?

So I finally got to enjoy my new sled today but I discovered it won't stay running at idle with the choke off. It will run fine with 1/2 choke (the warm up setting), including idle. In fact I can run the sled that way with no obvious bogging or stalling. Also i should note that Idle is only around 1200 at 1/2 choke. I expected it to be higher given that the manual says idle RPM should be 1800 which I assume is with no choke.

When I shut the choke off (after running for 10-15 minutes so its warm) RPMs drop off to about 500 and it runs for a few seconds, starts to sputter and just dies. Some times I can feather the throttle and keep it running and even run it at speed on the trail with the choke off if I'm careful not to let the RPMs drop off. Sometimes not.

Does this sound like a clogged carb or possible truly low idle since the manual says RPMs should be 1800 at idle. All the researching I did on stalling with choke off had symptoms of not running at all vs just not idling. So I'm not sure if it's not running at 1800 cause it's starved for fuel due to a clog or if I truly have a clog.

The guy I bought it from just had the carbs all cleaned and synced last fall but that was a year ago. I'm not sure a carb removal/cleaning is my cup of tea but I hate to bring it to the repair shop as they'll likely have it a while. I'm not sued what type of carbs I have either.

Any tips or thoughts are appreciated. Thanks!
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Old 12-30-2012, 08:06 PM   #2 (permalink)
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Clean the carbs out and pay close attention to the pilot circuit. Check out the carb cleaning stickie in the tech section of the forum.
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Old 12-30-2012, 09:10 PM   #3 (permalink)
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First thing to try is to just turn the idle screw a bit to increase the RPM. Take a look at the throttle cable and where it connects to the carb. There should be a knob to turn that will adjust all three carbs with the turn of a screw.
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Old 12-30-2012, 09:15 PM   #4 (permalink)
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While I agree with Dan that you should up the idle, I also second the opinion of Rczr600rider in cleaning the carbs. Even if your idle is low, it should be able to maintain that idle if it's getting enough fuel. Since you didn't say that opening the choke to half increase the idle speed, I'll presume it stays at 1200.

If it will idle at 1200 with the choke half on but not with the choke off, your carbs need to be cleaned so that the idle circuit will supply the necessary fuel.
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Old 01-01-2013, 08:21 AM   #5 (permalink)
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dive in and clean those carbs. the pilots are plugged. you run the risk of a burn down if you continue running the sled.

regardless of what was done last season, it doesnt take but a few weeks for todays fuel to gum up the carbs circuitry.
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Old 01-01-2013, 09:55 AM   #6 (permalink)
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Thanks everyone. I will get the carbs cleaned. Some friends with a lot more experience than me also checked it out yesterday. They agree, it's the carbs. They know someone who can get the sled in and out in just a few days. I don't want to risk damage, so I'll get it taken care of, along with having him do a once over of the whole sled.

Much appreciated.

Yamadad4, what do you mean by a "burn down?" I was told I could do damage if I do this too long (1/2 choke), but what does that term mean?
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Old 01-01-2013, 04:53 PM   #7 (permalink)
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Hole a piston or burn off the exhaust side causing much damage.
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Old 01-01-2013, 05:08 PM   #8 (permalink)
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Wow. Seriously? Running with a bit of choke could do that? I hope I haven't done anything already. Put may be 7 miles on it since it started doing this.
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Old 01-01-2013, 06:29 PM   #9 (permalink)
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its not so much the choke doing it as it is the fact that your lean on the pilot circuit. the choke is saving you at this point, but every time you forget to hit it your leaning out, creating excessive wear and opening yourself up to serious damage.

doesnt take anything but time to fix except a $2 can of carb spray or brakeclean. it can be alot more expensive if ignored.
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Old 01-01-2013, 06:48 PM   #10 (permalink)
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Everytime I forget to hit it? Forget to hit what? Man, I feel stupid!

I'm not ignoring it though. Calling a tech in the morning to bring it in...I'm not up for cleaning triple carbs and making sure they are in sync afterward.
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Old 01-01-2013, 06:55 PM   #11 (permalink)
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What yamadad4 is saying is this:

Your idle circuit in your carb is clogged. This is causing the fuel flow to be heavily restricted and makes what *is* there to be burnt too little. This is a lean condition, and that can destroy your motor because it essentially makes the combustion chambers way too hot and that "burns down" the piston and such.

When you put the choke on half way, you're adding fuel flow (which is a good thing in this case). The problem is, every time you jump on and throttle up WITHOUT opening the choke a bit, you're running the motor way too lean. So, if you forget to put the choke part way on, you're doing damage.
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Old 01-01-2013, 07:08 PM   #12 (permalink)
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the choke lever. at this point your using the choke as a crutch.

i am assuming that once your going your flipping it to the off position so the sled doesnt run pig rich with fuel. so then when you come to a stop or slow way down the sled wants to die, because its going lean. lean = more air, less fuel. fuel along with oil cools and lubricates the moving parts keeping them moving freely. heat expands things, oils keep them lubed.

on the flip side, too much fuel can actually wash the oils from the piston crown and prevent the lubeing necessary for the engines moving parts. by using the choke, your adding fuel to the combustion, taking away air.

hope that all made sense. not to worry, you have recognized the problem and taking care of it. you would be surprised how many neglect it because it "runs fine doing that" and they end up replacing pistons and even cylinders.
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Old 01-01-2013, 07:12 PM   #13 (permalink)
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good info there meburdick! you must type somewhat faster than myself, although i did fetch a beverage halfway through.

between the two, i think we shed some light!
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Old 01-01-2013, 07:14 PM   #14 (permalink)
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Thanks, YD4. I'm fairly proficient with the keyboard, but I think my read edge was in staying focused on the task. I, too, was very thirsty, but I powered through it.

lol
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Old 01-01-2013, 07:50 PM   #15 (permalink)
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Got it! Very helpful. Thanks.

But in my case, I wasn't really ever shutting the choke off, even once I got going, since it would die when I slowed or stopped without feathering (in which case sometimes it would still die). So I was just leaving it 1/4-1/2 on. So I rarely ran it with the choke off in this situation. And again, I've only used it twice now, since I discovered this, for not many miles. I'm guessing the previous owner didn't run it recently and that's why it's gummed up so I doubt he did this either. He thought low idle or something, which is why I asked about that.

I assume a qualified technician would be able to tell if all is ok after he gets it all tuned right again. Yes?

You guys are all great. I'm really enjoying learning about the sleds at this level.
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Old 01-01-2013, 07:53 PM   #16 (permalink)
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If he has a scope that he can drop into the cylinders through the plug wall, he'll be able to get a very good sense of the condition in there in a matter of a couple of minutes. Without a scope, he can give a decent idea as to whether there's any indication of it having been run lean for any period or not but likely can't tell you how the piston walls look.
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Old 01-10-2013, 08:59 AM   #17 (permalink)
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So just an update. Got the sled back last night. Had a friend go through it who fixes/tunes sleds on the side. He's been riding since he was 8 (he's about 40 now) and raced for a long time. He did a GREAT job. He said all 3 pilot circuits were clogged badly, and the exhaust valves were heavily crudded (is that a word) up. He cleaned everything, changed crankcase oil, adjusted track alignment and tension, chain tension, suspension, aligned the skis, etc. This thing runs unreal now! Very glad I had it done. Idles right around 1900-1700 now. Perfect!

Thanks for all the help. I thought an update was in order.
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Old 01-10-2013, 09:08 AM   #18 (permalink)
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That's great to hear.

One thing of note - if he changed the crankcase oil, he's not much of a friend (that would be like him changing the headlight fluid). I think you meant chaincase oil.

It sounds like he attended to all of the very common things that need to be attended to. Enjoy, and ride safe!
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Old 01-10-2013, 09:17 AM   #19 (permalink)
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Chaincase, yes! Used synthetic oil, and adjusted the chain tension etc, greased everything, washed it! He's a great guy and an awesome sled tech. He eats, sleeps and, well, you know, sleds.
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Old 01-10-2013, 10:38 AM   #20 (permalink)
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Now you need to learn how to do everything that he did, 'cause you should do it yearly

glad it's working, it's awesome having sleds that run right
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